Camshaft phasers for varying the timing of combustion valves in internal combustion engines are well known. A first element, known generally as a sprocket element, is driven by a chain, belt, or gearing from the internal combustion engine's crankshaft. A second element, known generally as a camshaft plate, is mounted to the end of an internal combustion engine's camshaft. A common type of camshaft phaser used by motor vehicle manufactures is known as a vane-type camshaft phaser. U.S. Pat. No. 7,421,989 shows a typical vane-type camshaft phaser which generally comprises a plurality of outwardly-extending vanes on a rotor interspersed with a plurality of inwardly-extending lobes on a stator, forming alternating advance and retard chambers between the vanes and lobes. Engine oil is supplied via a multiport oil control valve, in accordance with an engine control module, to either the advance or retard chambers, to change the angular position of the rotor relative to the stator, and consequently the angular position of the camshaft relative to the crankshaft, as required to meet current or anticipated engine operating conditions.
While vane-type camshaft phasers are effective and relatively inexpensive, they do suffer from drawbacks. First, at low engine speeds, oil pressure tends to be low, and sometimes unacceptable. Therefore, the response of a vane-type camshaft phaser may be slow at low engine speeds. Second, at low environmental temperatures, and especially at engine start-up, engine oil displays a relatively high viscosity and is more difficult to pump, therefore making it more difficult to quickly supply engine oil to the vane-type camshaft phaser. Third, using engine oil to drive the vane-type camshaft phaser is parasitic on the engine oil system and can lead to requirement of a larger oil pump. Fourth, for fast actuation, a larger engine oil pump may be necessary, resulting in additional fuel consumption by the internal combustion engine. Lastly, the total amount of phase authority provided by vane-type camshaft phasers is limited by the amount of space between adjacent vanes and lobes. A greater amount of phase authority may be desired than is capable of being provided between adjacent vanes and lobes. For at least these reasons, the automotive industry is developing electrically driven camshaft phasers. Electrically driven camshaft phasers include a gear drive unit having an input gear member and an output gear member. Rotation of the input gear member by the electric motor causes relative rotation between the input gear member and the output gear and consequently a change in phase relationship between the crankshaft and the camshaft.
One type of electrically driven camshaft phaser being developed uses a harmonic drive gear unit, actuated by an electric motor, to change the angular position of the camshaft relative to the crankshaft. Examples of such camshaft phasers are shown in U.S. Pat. Nos. 5,417,186; 6,328,006; 6,257,186 and 7,421,990. In each of these examples, an electric motor includes a motor shaft which is coupled to an input member of the harmonic gear drive unit by inserting the motor shaft within a bore of the input member. The motor shaft is prevented from rotating relative to the harmonic drive input member by pinning the shaft to the input member or by using a key and keyway. While these attachment methods are simple, they does not allow for misalignment of the motor shaft and the bore of the input member of the harmonic drive gear unit.
United States Patent Application Publication No. US 2011/0030631 A1, which is assigned to Applicant and incorporated herein by reference in its entirety, also teaches an electrically driven camshaft phaser using a harmonic drive gear unit, actuated by an electric motor, to change the angular position of the camshaft relative to the crankshaft. However, unlike the previous examples, the electric motor includes a coupling pinned to its motor shaft. The coupling includes opposing male drive lugs which interfit with female drive slots formed in a coupling adapter which is attached to the input of the harmonic gear drive unit. The female drive slots are formed in a portion of the coupling adapter which extends axially away from/axially adjacent to a press fit surface of the coupling adapter. The press fit surface receives a bearing in a press fit manner to radially support the coupling adapter within a housing. It may be undesirable to position the female drive slots radially under the press fit surface to decrease the axial length because doing so may compromise the bearing press fit. Consequently, the axial length of the camshaft phaser is lengthened due to the need for the female drive slots to be positioned axially away from the bearing press fit area.
What is needed is an electrically driven camshaft phaser with an axially compact coupling for joining an electric motor to a gear drive unit; more particularly to such a camshaft phaser in which the gear drive unit is a harmonic gear drive unit; and even more particularly to such a camshaft phaser in which the coupling adapter allows for misalignment between the axis of rotation of the electric motor and the axis of rotation of an input gear member of the gear drive unit.